The pulse tube cryocoolers do not have moving parts under a low temperature, and have advantages of a simple structure, low cost, low mechanical vibration, high reliability, and a long life. These advantages make the research of pulse tube cryocoolers popular. Compared with G-M type pulse tube cryocoolers, Stirling type pulse tube cryocooler is smaller and more compact, hence attracts more attention. As the enthalpy phase modulation theory indicates, the phase difference between the mass flow and the pressure wave can significantly affect the cooling performance of the pulse tube cryocooler. Thus, it is crucial to choose appropriate device for phase modulation. There are three kinds of phase modulation for pulse tube cryocoolers at present, namely the orifice, the double inlets and the inertance tube. Compared to the orifice, the inertance tube uses the inertance effect of the oscillating gas inside a long and thin tube to adjust the phase difference, which has better performance and wider range of phase modulation. Compared with the method of using double inlets, there are no direct current flows inside the inertance tube. This can eliminate the vibration at the cold end of the pulse tube caused by the direct current flow. Therefore, the inertance tube for phase modulation is better for Stirling type high-frequency pulse tube cryocoolers.
Researches by Radebaugh and some other people indicate that: when the phase of the mass flow and pressure wave in the middle of the regenerator is the same, the cooling efficiency of the pulse tube cryocooler is the highest. At the same time, at the hot end of the regenerator, the phase of the mass flow leads in advance the phase of the pressure wave about 30 degrees. And at the cold end, the phase of the pressure wave lags the phase of the mass flow about 30 degrees. These combined means that at the inlet of the inertance tube, the phase of the mass flow should lags the pressure wave about 60 degrees. Therefore, the inertance tube should be capable of at least 60 degrees of phase modulation. But for pulse tube cryocoolers which have smaller PV work, it is not realistic to realize that the phase of the mass flow lags the pressure wave about 60 degrees. Thus, it is urgently necessary to increase the acoustic power at the hot end of pulse tube and will improve the phase modulation capability of the inertance tube, in order to provide a proper angle for pulse tube cryocoolers.
For an ideal regenerator, the ratio of the acoustic power at the hot end to the acoustic power at the cold end is proportional to the ratio of the temperature at the hot end to the cold end. According to this principle, putting regenerative materials inside the pulse tube at proper position will function as an acoustic power amplifier for the cold end. This is the core content of the present invention, which will offer necessary phase modulation for the inertance tube at the hot end in the pulse tube.